Magnetic fluid display device

ABSTRACT

An immiscible, transparent fluid and an opaque magnetic fluid are contained within a defined volume, such as a sandwich-type construction having a transparent face through which an optical display may be observed. The transparent fluid preferentially wets the wall and results in complete displacement of opaque fluid when the fluids are moved one to the other. A magnetic field captures the magnetic fluid in a predetermined optical pattern. The optical pattern is controlled by varying the intensity and location of the magnetic field to produce various patterns.

03417-72 xa awasgzw o Umted States Patent [151 3,648,269

Rosenweig 'et al. 1 Mar. 7, 1972 [54] MAGNETIC FLUID DISPLAY DEVICE2,891,242 6/1959 Lukoff ..340/373 [72] Inventors: Ronald Rosenweig,Lexington Mass; 3,229,281 1/1966 Hackenfort ..340/373 Joseph Resnickdeceased late of New 3,292,171 12/1966 Wilson ..340/324 R York NY; LouisBerger, executor; Harry 3,322,482 5/1967 Harmon ..350/267 Resnick,executor; Peter Mesh, exam 3,328,110 6/1967 Berger et al.. ....350/l51 Xtor, all f Ellenvme N Y 3,560,956 2/1971 Smnott "340/324 R 3,572,8963/1971 Bertram ..350/267 [73] Assignee: Ferrofluidics Corporation,Burlington,

Mass- Primary Examiner-David L. Trafton 22 Filed: n, 1 1970Attorney-Richard P. Crowley and Richard L. Stevens [21] App1.No.: 55,392[57] ABSTRACT An immiscible, transparent fluid and an opaque magneticfluid [52] US. Cl. ..340/373, 340/324 R, 350/267, are contained within adefined volume such as a sandwich [5 l t Cl type construction having atransparent face through which an I! optical p y may be observed htransparent fluid [58] Field of Search "340/324 373; preferentially wetsthe wall and results in complete displacel9 ment of opaque fluid whenthe fluids are moved one to the other. A magnetic field captures themagnetic fluid in a [56] References Cited predetermined optical pattern.The optical pattern is con- UNITED STATES PATENTS trolled by varying theintensity and location of the magnetic l 835 612 12ll931 P 350/267 fieldto produce various patterns.

earson 1,963,496 6/ 1934 Land ..350/267 X 21 Claims, 13 Drawing FiguresNSNSNSNS atented March 7, 1972 3,648,269

o b c d e f W J ON OFF 0 b :3 D=. 6 INVENTOR SNSNSNSN- BY ATTORNEYMAGNETIC FLUID DISPLAY DEVICE SUMMARY OF THE INVENTION This inventionrelates to optical displays in which optical patterns may be controlledby varying a magnetic field which acts upon a quantity of an opaquemagnetic fluid. The magnetic fluid may be used to form patterns oralternatively to unveil graphic symbols imprinted on a surface. Theinvention performs a function which permits changes in shape, position,and state of subdivision of an opaque curtain, for example into separatepools or droplets. Subsequently, the curtain may be combined again intoa single coherent area. In other words, the invention produces a changeof shape or a reversible subdivision of a fluid with a degree of controlnot heretofore possible. Further the invention utilizes the phenomenonof preferential wetting of a surface by an appropriate nonmagneticfluid. Briefly, the invention comprises a combination of a magneticfluid and an immiscible nonmagnetic fluid one of the fluids being of onecolor and the other of a clearly distinquishable color or the magneticfluid being opaque while the immiscible carrier fluid is relativelytransparent. The fluids are contained within a defined volume such aswithin a sandwich-type construction. One of the faces of suchconstruction is transparent whereby the various patterns formed by themagnetic fluid within the construction may be readily viewed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan front view of oneembodiment of the inventron;

FIG. 2a is a schematic sectional view of FIG. 1 taken along lines 2-2 ofFIG. 1;

FIG. 2b is a sectional view of an alternative embodiment of FIG. 2a;

FIGS. 3a through f are schematic illustrations of various displays whichmay be achieved with the invention;

FIG. 4 is a schematic illustration of the invention demonstrating itsuse to reveal graphic messages or designs on a particular surface;

FIGS. 5a and b are schematic illustrations of the invention wherein apermeable shield is used to vary the display pattern rather than varyingthe magnetic field; and

FIG. 6 is a sectional view of FIG. 5a.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, theinvention is shown generally at 10 and comprises an upper transparentsurface 12 spaced apart from a lower surface 14 by a rectangular-shapedspacer l6. Disposed within the space defined by the surfaces 12 and 14and spacer 16 is a magnetic fluid 18 and a transparent, immiscible fluid20. Spaced apart from the surface 14 is a magnetic array 22 which isspecially designed for compactness and to create short-range magneticfields with large field gradients. If desired the magnetic array may bedisposed within one of the surfaces. The magnetic array captures a thinfluid layer of relatively uniform thickness in any desired area. Asshown in FIG. 2a, the magnetic fluid does not extend from one to theother surface. However, if desired, it may extend from one to the othersurface as shown in FIG. 2b.

In FIG. 3a the pattern of the magnetic fluid reveals the size andconfiguration of the underlying magnetic field. In FIG. 3b the magneticfield and hence the pattern established by the magnetic fluid has beenrotated by 45. FIG. 30 depicts the translation of the pattern when themagnetic field is moved. The pattern as shown in FIG. 3d results in adistribution of drops when the magnet is oscillated rapidly or if theframe is vibrated vigorously. FIG. 32 shows the fluid falling under'theforce of gravity when the magnetic field is removed and FIG. 3f is theequilibrium of the fluids in the presence of gravity alone. Byimprinting a graphic message or design on the surface 14 and providingthe magnetic fluid on one side of the surface as shown and the magneticsource on the other the unique arrangement of veiling and unveiling theimprinted message of design is achieved simply by varying the positionof orientation and characteristics of the magnetic sources achieved. Asshown in FIG. 4, this arrangement could be used to indicate the presenceor absence of a particular electrical current. For example, the magnetbehind the surface could be an electromagnet and when the circuit hasbeen actuated or is live then the magnetic fluid would be positioned asshown revealing the letters on" indicating the flow of current through aparticular circuit. When the current through the circuit isdiscontinued, then the magnetic fluid would fall by gravity to theposition indicated in FIG. 3c to reveal the work off indicating that nocurrent is passing through the circuit. Alternatively, the fluid can belocated by a permanent magnetic field, moved by an electromagnetic fieldand returned by the permanent magnetic field with no additionalconsumption of power.

The magnet may be positioned by hand, by a motorized drive, by a float,by an acoustical transducer or any other means of displacement. Amagnetic imprint on a moving tape may be used to display messages thatmove across the display unit. Various colored and reflecting backgroundsenhance the graphic displays. The graphics may be combined on the frontor back surface of both plates and the displays may be used in flat,cylindrical, spherical or other geometries. By using electromagnetsand/or the fields surrounding current carrying wires, the pattern may becontrolled either by motion of the magnetic field source or by switchingthe currents or a combination of the two. Alphanumeric displays may alsobe created.

FIG. Sshows the effect when a permeable sheet of any shape, but as shownin the shape of the letter E, is inserted between the magnet andmagnetic fluid and is effective in shielding the applied field locally.As shown, FIG. 5a shows the pattern established by the magnet andmagnetic fluid before the insertion of the permeable shield and FIG. 5billustrates the resulting pattern when the permeable shield has beenpositioned. Also with the permeable shield, other patterns may beobtained by rotation or translation of the permeable shield rather thanthe magnet field source.

The material used in the invention, that is the magnetic and nonmagneticfluids and the substrate wall, should possess the desired properties ofpreferential wetting. Any type of magnetic fluid may be used with theinvention and this would include those magnetic fluids which comprise acarrier fluidlike water, hydrocarbons, fluorocarbons, etc., a surfaceactive agent such as fatty acids, for example a mono-unsaturated fattyacidlike oleic acid, and any other type particles such as ferrousmaterials like ferrite, chromium dioxide, magnetite etc. The immisciblefluid used with the magnetic fluid should first be immiscible with themagnetic fluid, must preferentially wet the substrate, and further inmost cases it is desired that it have a density which approaches that ofthe magnetic fluid for easier positioning of the fluid when the magneticfluid is moving in relation to the immiscible fluid by the applicationof various magnetic fields. Useful immiscible fluids which may be usedwith waterbase magnetic fluids are silicone fluids, hydrocarbonmaterials such as mineral oil, carbon tetrachloride, combinations of thesame and other similar materials for a wall that is composed of glass orpolystyrene.

Although the invention has been described in general with reference tothe magnetic fluid being opaque and the immiscible fluid beingtransparent, the magnetic fluid if desired may be transparent and theimmiscible fluid opaque. Useful combinations of magnetic fluids,immiscible fluids and surface substrates which may be used are: awater-base ferrofluid, mineral oil, and glass; a water-base ferrofluid,mineral oil, and polystyrene; a water-base ferrofluid, silicone, andglass; a water-base ferrofluid, silicone, and polystyrene; akerosenebase ferrofluid, water with a water soluble surfactant agentsuch as sodium lauryl sulfate, and glass; and a fluorocarbonbaseferrofluid, water and a water soluble surfactant agent, and glass.

Having described the invention, what we now claim is:

I. A magnetic fluid display device which comprises:

a. a magnetic fluid;

b. an immiscible fluid in combination therewith;

c. means to retain the magnetic fluid and the immiscible fluid within apredetermined volume, said means including a surface adapted to bepreferentially wetted by the immiscible fluid; and

d. magnet means to control the movement of the magnetic fluid throughthe application of a magnetic field whereby a predetermined opticalpattern is established.

2. The device of claim 1 wherein the means to retain the fluids includesfirst and second surface means, a portion of one of said surfaces beingtransparent, spacer means disposed between said surfaces and defining incombination with said surfaces the predetermined volume.

3. The device of claim 1 wherein the magnet means is spaced apart fromthe means to retain the fluids.

4. The device of claim 1 wherein the magnetic fluid is opaque and theimmiscible fluid is transparent, the means to retain the fluids includesa first transparent plate: and a second plate in spaced apartrelationship, the second plate having a patterned surface thereonadapted to be viewed through the transparent plate whereby throughmovement of the magnet means the magnetic field may be caused to maskand unmask the pattern.

5. The device of claim 1 wherein the fluids are of distinct colorations.

6. The device of claim 5 wherein the magnetic fluid is opaque and theimmiscible fluid is transparent.

7. The device of claim 1 which includes means to interpose a barrierbetween magnet means and the magnetic fluid whereby the patternestablished by the magnetic field is varied.

8. A method for displaying visual patterns which comprises:

a. providing a device containing therein a magnetic fluid and animmiscible fluid and having a surface adapted to be wettedpreferentially by an immiscible fluid;

b. creating a magnetic field;

c. capturing the magnetic fluid in the magnetic field to provide apredetennined optical pattern; and

d. varying the magnetic field to provide various optical patterns.

9. The method of claim 8 wherein the magnetic fluid is opaque and theimmiscible fluid is transparent.

10. The method of claim 8 which includes magnet means to create themagnetic field.

11. The method of claim 8 which includes rotating the magnetic fieldsource to provide the varied optical pattern.

12. The method of claim 8 which includes interposing within the magneticfield magnetically permeable barrier means to vary the optical pattern.

13. The method of claim 8 which includes providing a first surfacehaving a pattern thereon, providing a second surface spaced apart fromthe first surface said second surface being transparent whereby varyingthe magnetic field as to intensity and position the visual patternobserved is also varied.

14. The method of claim 13 wherein one surface of the nontransparentsurface has a predetermined visual pattern thereon and which includesvarying the location of the opaque magnetic fluid within thepredetermined volume to mask and unmask the pattern whereby it may bereadily observed.

15. The method of claim 8 wherein the magnetic fluid is a water-basemagnetic fluid, the immiscible fluid is a mineral oil and the surface isglass.

16. The method of claim 8 wherein the magnetic fluid is a water-basemagnetic fluid, the immiscible fluid is a hydrocarbon oil and thesurface is polystyrene.

17. The method of claim 8 wherein the magnetic fluid is a water-basemagnetic fluid, the immiscible fluid is silicone and the surface isglass.

18. The method of claim 8 wherein the magnetic fluid is a water-basemagnetic fluid, the immiscible fluid is silicone and the surface ispolystyrene.

19. The method of claim 8 wherein the magnetic fluid is a kerosene-basemagnetic fluid, the immiscible fluid is water in combination with asurfactant agent and the surface is glass.

20. The method of claim 19 wherein the surfactant agent 15 sodium laurylsulfate.

21. The method of claim 8 wherein the magnetic fluid is afluorocarbon-base magnetic fluid, the immiscible fluid is water incombination with a surfactant agent and the surface is glass.

1. A magnetic fluid display device which comprises: a. a magnetic fluid;b. an immiscible fluid in combination therewith; c. means to retain themagnetic fluid and the immiscible fluid within a predetermined volume,said means including a surface adapted to be preferentially wetted bythe immiscible fluid; and d. magnet means to control the movement of themagnetic fluid through the application of a magnetic field whereby apredetermined optical pattern is established.
 2. The device of claim 1wherein the means to retain the fluids includes first and second surfacemeans, a portion of one of said surfaces being transparent, spacer meansdisposed between said surfaces and defining in combination with saidsurfaces the predetermined volume.
 3. The device of claim 1 wherein themagnet means is spaced apart from the means to retain the fluids.
 4. Thedevice of claim 1 wherein the magnetic fluid is opaque and theimmiscible fluid is transparent, the means to retain the fluids includesa first transparent plate and a second plate in spaced apartrelationship, the second plate having a patterned surface thereonadapted to be viewed through the transparent plate whereby throughmovement of the magnet means the magnetic field may be caused to maskand unmask the pattern.
 5. The device of claim 1 wherein the fluids areof distinct colorations.
 6. The device of claim 5 wherein the magneticfluid is opaque and the immiscible fluid is transparent.
 7. The deviceof claim 1 which includes means to interpose a barrier between magnetmeans and the magnetic fluid whereby the pattern established by themagnetic field is varied.
 8. A method for displaying visual patternswhich comprises: a. providing a device containing therein a magneticfluid and an immiscible fluid and having a surface adapted to be wettedpreferentially by an immiscible fluid; b. creating a magnetic field; c.capturing the magnetic fluid in the magnetic field to provide apredetermined optical pattern; and d. varying the magnetic field toprovide various optical patterns.
 9. The method of claim 8 wherein themagnetic fluid is opaque and the immiscible fluid is transparent. 10.The method of claim 8 which includes magnet means to create the magneticfield.
 11. The method of claim 8 which includes rotating the magneticfield source to provide the varied optical pattern.
 12. The method ofclaim 8 which includes interposing within the magnetic fieldmagnetically permeable barrier means to vary the optical pattern. 13.The method of claim 8 which includes providing a first surface having apattern thereon, providing a second surface spaced apart from the firstsurface said second surface being transparent whereby varying themagnetic field as to intensity and position the visual pattern observedis also varied.
 14. The method of claim 13 wherein one surface of thenontransparent surface has a predetermined visual pattern thereon andwhich includes varying the location of the opaque magnetic fluid withinthe predetermined volume to mask and unmask the pattern whereby it maybe readily observed.
 15. The method of claim 8 wherein the magneticfluid is a water-base magnetic fluid, the immiscible fluid is a mineraloil and the surface is glass.
 16. The method of claim 8 wherein themagnetic fluid is a water-base magnetic fluid, the immiscible fluid is ahydrocarbon oil and the surface is polystyrene.
 17. The method of claim8 wherein the magnetic fluid is a water-base magnetic fluid, theimmiscible fluid is silicone and the surface is glass.
 18. The method ofclaim 8 wherein the magnetic fluid is a water-base magnetic fluid, theimmiscible fluid is silicone and the surface is polystyrene.
 19. Themethod of claim 8 wherein the magnetic fluid is a kerosene-base magneticfluid, the immiscible fluid is water in combination with a surfactantagent and the surface is glass.
 20. The method of claim 19 wherein thesurfactant agent is sodium lauryl sulfate.
 21. The method of claim 8wherein the magnetic fluid is a fluorocarbon-base magnetic fluid, theimmiscible fluid is water in combination with a surfactant agent and thesurface is glass.